It is often necessary to damp low-frequency vibrations, e.g. vibrations having a frequency lying between a few hertz and a few tens of hertz, and appearing in structures along a predetermined direction, exerting non-negligible stresses thereon. In contrast, in certain cases, it is desirable to be able to create large-amplitude low-frequency vibrations in a structure along a given direction, with such vibrations being used for various purposes, e.g. sorting or cleaning, in addition to simulating or compensating vibratory phenomena.
Various types of unidirectional vibrators capable of generating or damping vibrations at a predetermined frequency already exist. However, these actuators often have a moving member of small mass or having limited displacement possibilities, e.g. about 1 millimeter, thus making it impossible to create forces that are large enough for generating or damping vibrations at a low frequency of around a few hertz.
Thus, vibrating pots are known which generate relatively high-frequency vibrations and which include an outlet fixed to a small cantilevered moving mass and provided with a small coil disposed in the air gap of a permanent magnet which is itself connected to a frame by means of springs. Such an actuator having a small moving mass is suitable only for use at frequencies of at least several hundreds of hertz and it also suffers from drawbacks insofar as the suspension and moving mass assembly is not very rigid, thus making the device highly sensitive to lateral shocks.
More generally, prior vibrating pots constitute relative vibrators which create forces between a stator and an outlet, in contrast to an absolute vibrator which has a free mass with the reaction forces on the stator or the frame of an absolute vibrator being used to create the required forces. Vibrating pot type relative vibrators remain fragile and difficult to use.
One example of a known free mass absolute vibrator is constituted by an omnidirectional vibrator having a spherical free body mounted by means of electromagnets inside a housing which is thus capable of creating forces in three different directions. However, such a vibrator is a high-frequency device and must have small air gaps, which means it cannot accommodate displacements exceeding about 1 millimeter.
The present invention seeks to remedy the above-mentioned drawbacks and to provide a vibrator device constituting a large-amplitude actuator capable of acting on structures in a given direction over a range of low frequencies, exerting large forces without being sensitive to lateral shocks.